Recently, a wind energy is actively introduced as one of renewable energies. The wind energy is an unstable energy that varies with a variation in a wind speed. Therefore, in a case where the wind energy is interconnected with a power system without consideration of its variation, there is a risk that stable supply of a power is hindered. For a system interconnection of the wind energy, regulations on a variation width of the wind energy, for example, are provided in order to suppress a variation in the power supplied to the power system.
There is known a technique in which a wind power generation apparatus and a power storage apparatus are provided together, as a technique for suppressing the variation in the power supplied to the power system. The power storage apparatus stores (that is, charges) a generated power of the wind power generation apparatus and supplies (that is, discharges) the stored power to the power system, for absorbing a variation in the generated power of the wind power generation apparatus.
However, the conventional technique cannot cause the power storage apparatus to store or supply the power without excess or deficiency, while sufficiently considering a long-term change in a capacity of the power storage apparatus. Therefore, there is a problem that a shortage of the capacity of the power storage apparatus while the power storage apparatus supplies the power causes difficulty in suppressing the variation in the power supplied to the power system, for example.